1. Field of the Invention
The present invention relates generally to devices and procedures used during orthopedic surgery. An embodiment relates to bone lengthening by distraction osteogenesis.
2. Description of Related Art
Some people may have one or more shortened limbs due to short bone length in the affected limbs. Short bone lengths may be due to birth defects, disease, and/or injury. Distraction osteogenesis may be used to elongate a short bone. Distraction osteogenesis may involve a separation phase, an activation phase, and a consolidation phase. During the separation phase, a bone that is to be elongated may be cut at a selected location to separate the bone into two pieces. The bone pieces may be stabilized relative to each other with a separation mechanism. A callus may form between the ends of the two bone pieces. During the activation phase, the bone pieces may be gradually separated using a separation mechanism. The separation mechanism may separate the bone pieces at a rate of approximately 1 millimeter (mm) per day. Gradual separation of the bone pieces may result in slow stretching of the callus. Slow stretching of the callus may result in the formation of additional callus at an interface between the bone pieces. In addition, gradual stretching of the callus may allow neurovascular bundles and muscles to adjust in position and/or length. After a desired length of the bone is obtained, separation of the bone pieces may be stopped. A consolidation phase may ensue. During the consolidation phase, the separation mechanism may be left in position to provide support to the forming bone and remaining portions of callus.
Distraction osteogenesis was pioneered by the Soviet orthopedic surgeon Dr. Gavriel Ilizarov. Ilizarov lengthened the limbs of dwarfs up to eighteen inches using bicycle sprockets and spokes to form extendable cages fitting externally over the patient's limbs. The distal end of the cage was incrementally extended from the proximal portion mechanically. A plurality of pins was inserted through the muscle of the limb, and into both portions of the bone. With the proximal portion of the limb “anchored” by the pins in the cage, force was transmitted through the pins to pull the distal portion away from the anchored portion. This type of device required numerous incisions in a limb for the pins. The incisions were susceptible to infection and the pins were continually pulling on flesh. Furthermore, wearing a cage over a period of months severely limited the mobility of the patient.
Various distracting means have been developed, such as external fixators, in which each segment of bone is transfixed by pins or wires coupled to clamps, which are then distracted. Examples of external fixator systems include: (i) bilateral frames, for which fixator bodies or rods are located one on each side of the bone being transfixed, (ii) unilateral frames, for which only a single fixator body or rod is located to one side of the bone, and (iii) ring fixators, for which a series of rings are spatially arranged around the limbs so as to form a cylinder, the rings being interconnected by struts.
The applications of lengthening procedures using external fixators have been limited due to a high rate of complications, including wire site infection, bone infection, pain, scarring, patient discomfort, and restricted joint motion due to the transfixation of tendons and muscles.
Many of the associative complications with external distraction devices, such as external fixators, were eliminated when internal distraction devices were introduced. Schollner reported using a distraction device implanted adjacent to the bone being lengthened. (Schollner, D., New ways of operating to lengthen the femur, Z. Orthop. 110:971-974 (1972) citing Anderson, W. V., Leg lengthening, J. Bone Joint Surg. [Br] 34-b:150 (1952)). Gotz and Schellmann described studies on a hydraulic distractor placed in a modified interlocking nail. (Gotz, J., Schellmann, W. D., Continuous lengthening of the femur with intramedullary stabilization, Arch. Orthop. Unfall-Chir. 82:305-310 (1975)). According to Gotz and Schellmann, a cylinder external to the bone supplied hydraulic pressure to an internal nail. Baumann and Harms reported using a telescoping nail driven by a threaded spindle transcutaneously attached to the nail. (Baumann, F., Harms, J., The extension nail. A new method for lengthening of the femur and tibia, Arch. Orthop. Unfall-Chir. 90:139-146 (1977)).
Witt et al. were the first to report human clinical results from a completely implantable femur distractor. (Witt, A. N., Jager, M., Bruns, H., Kusswetter, W., Hildebrant, J. J., Die operative Oberschenkelverlangerung mit einem vollimplantierbaren Distraktionsgerat, Arch. Orthop. Traumat. Surg. 92:291-296 (1978)). Witt et al. reported implanting a device in the soft tissue adjacent to the bone and screwing the device into the femur proximally and distally. Witt et al. used an electric motor housed in the device to generate a distraction force. The motor is controlled by telemetry from outside the body, providing for both forward and backward motion.
Betz et al. disclosed a fully implantable intramedullary system for lengthening bones, using telemetry to control an electric motor in U.S. Pat. No. 6,245,075. Betz et al. developed two variants of an intramedullary nail, one with implanted energy and control units, and one with external energy and control units. The first device utilizes a battery pack and a telemetry receiver, which are both implanted subcutaneously, with an automatic controller. The second device uses only a receiver that is implanted and connected to the driving motor, allowing for a much smaller subcutaneous packet. The patient attaches a telemetry sender to his leg during the night, which activates the device and transmits the energy to the motor. According to the teachings of Betz et al., both devices use an electric motor to provide a distraction force.
Pursley disclosed two embodiments of an intramedullary telescoping distractor in U.S. Pat. No. 5,156,605. Like the device of Betz et al., both embodiments require a distraction force be provided using an electric motor and controller to drive a lead screw. According to the first embodiment, the motor is housed outside the body and connected to the internal tube by means of a flexible shaft. In the second embodiment, the motor and control units are internally mounted and controlled by a communication assembly from outside the body.
Other limited reports of work on internal lengthening devices include Herzenberg, J. E., Hensinger, R. N., Goldstein, S. A., Michigan intramedullary leg lengthening nail, in: Biomechanics, Trauma and Sports Medicine Laboratory Annual Report, University of Michigan (1989); Verkerke, G. J., Koops, H. S., Verb, R. P. H., Nielsen, H. K. L., Design of a load cell for the Wagner distractor, Proc. Instn. Mech. Engrs. 203:91-96 (1989); Fisher, C., personal communication., Feb. 12, 1992; and Hellend, P., Femoral elongation by use of an elongable intramedullary device, Acta Orthop. Scand. 63(Suppl. 247):16 (1992).
An implantable distraction device designed for a long bone may provide the capability of: (1) a low profile around the bone, (2) structural stability when attached to the bone to prevent bending movement, (3) an economical construction, and (4) distraction without the risk of infection by percutaneous wounds or significant scarring.